Wiring external devices in an intrinsically safe area (multiple barriers)Figure 3-12:
Hazardous Area
Non-Hazardous Area
24 VDC
MTL7728P+
Barrier 3
Barrier 1
Barrier 2
3
4
1
2
A
B
C
E
Bus
Bar
mA1+
HART
D
A. HART Device 1
B. HART Device 2
C. HART Device 3
D. Meter (mA+/HART output)
E. HART/Field Communicator
CAUTION!
• In an electrically noisy environment, screen the cable in a safe area.
• To meet the EC Directive for Electromagnetic Compatibility (EMC), use a suitable instrumentation cable to connect
the meter. The instrumentation cable should have individual screens, foil or braid over each twisted pair, and an
overall screen to cover all cores. Where permissible, connect the overall screen to earth at both ends (360° bonded
at both ends). Connect the inner individual screens at only the controller end.
• For safety, do not terminate the inner individual screens to earth in a hazardous area.
• Use metal cable glands where the cables enter the meter amplifier box. Fit unused cable ports with metal
blanking plugs.
Wiring
Installation Manual 37
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